Yes, removing that is absolutely OK. 
The "core_test" bundle is no longer a plugin, but a plugin *fragment* of the "core" bundle. This means that the Require-Bundle parameter is no longer needed and in fact Eclipse complains with warning about that, therefore I removed it.

As for why core_test is a fragment now, this is a best practice regarding packaging JUnit tests in an OSGi environment. Fragment bundles have full access to the classes of their fragment-host bundle (they share a common classloader), so if you like to unit test internal classes, you no longer have to artificially make a public API just for the purposes of unit testing.